Tube reducing machine



Nov. 18, 1969 A. F. TREMBLAY TUBE REDUCING MACHINE 5 Sheets-Sheet 1Filed July 28, 1967 .Y R T mL T E A WE fi F T H E mm A Nov. 18, 1969 A.F. TREMBLAY 3,478,557

TUBE REDUCING MACHINE Filed July 28, 1967 5 Sheets-Sheet 2 ALBERT E TREMBLAY.

ATTYS,

Nov. 18, 1969 A. F. TREMBLAY TUBE REDUCING MACHINE 5 Sheets-Sheet 5Filed July 28, 1967 ATTYE'.

Nov. 18, 1969 A. F. TREMBLAY 3,478,557

TUBE REDUCING MACHINE 5 Sheets-Sheet 4 Filed July 28, 1967 I INVENTOR.ALBERTF IHEMBLAK QMQW ATTYS.

United States Patent US. Cl. 72-189 13 Claims ABSTRACT OF THE DISCLOSUREA tube reducing machine is provided which has large diameter dies anddie holders supported in a stationary frame. The machine includesrelatively simple components for movably' supporting the die holdersrelative to the frame of the machine and yet enabling the die holders tomove with forward and rearward coordinated strokes without the necessityof moving the frame back and forth. The die holders carry gear segmentswhich are engaged with one another to synchronize movement thereof, withone of the gears also being engaged with a gear rack to further controlmovemnt of the die-holders. The tube reducing machine also has a uniquedrive arrangement by means of which only one of the die holders isdriven, with a linkage connection arranged between the die holders tomove the second holder with the first. The dies of the machine also areadjustably mounted in the die holders so as to be accurately positioned,adjusted for wear, and adjusted to produce a precise final dimension ofthe tube.

This application is a continuation-in-part of my copending applicationSer. No. 459,661 filed on May 28, 1965, now Patent No. 3,357,223.

This invention relates to a tube reducing machine having improvementsparticularly in the supporting arrangement for the die holders and inthe drive therefor.

Tube reducing machines generally have included a pair of mating dierolls mounted in a reciprocating frame or saddle supported forreciprocation in a path parallel to the axis of the tube being rolledand reduced. Such saddles were necessarily massive to withstand thepressures involved in the cold forming operation, and the power requiredto reciprocate the saddles was substantial. Also the number of strokesper unit of time which could be achieved was quite limited.

For some tube reducing machines heretofore proposed, relatviely largediameter dies have been suggested which were rocked back and forththrough relatively small angles and held by a stationary frame. However,with the manner in which these rolls were supported and driven, asubstantial amount of sliding or skidding contact occurred between thedies and the tube. This resulted in rapid die wear as well as skid markson the surfaces of the finished product. A considerable amount of heatalso was produced with consequential loss of power.

While certain tube reducing machines have been proposed in the art whichsupport and rock the dies back and forth in a manner to produce arelatively small ice amount of sliding, such machines have incorporatedunduly complicated supporting and drive mechanisms which have renderedthe machines costly and increased the maintenance problems thereof.Further, the dies of such machines have engaged the tube being reducedduring only one stroke of the dies, being separated from the tube uponthe return stroke. Of necessity, this substantialy reduced theproduction rate of the machines.

The present invention relates to an improved tube reducing machinehaving many advantages over those heretofore known. The new machineincorporates a pair of large diameter dies mounted in a stationaryframe, rather than a reciprocating one, and with simplified supportingcomponents for the dies and die holders. The components, even thoughuncomplicated, are designed so that the rolls have little tendency toslide on the tube. The machine also employs an arrangement forcoordinating the rocking movements of both die holders relative to oneanother as well as coordinating them relative to the frame to maintainclose control over their movements. The drive arrangement for the dieholders of the new machine also is unique. Only one of the die holdersis directly driven while the second is indirectly driven through a novellinkage arrangement connected with the first die holder. With this,there is no necessity of precisely coordinating drive mechanisms forreach of the die holders as has heretofore been the case. The dies ofthe new machine preferably are recessed slightly in the die holders sothat the dies never come in contact with one another. This substantiallyreduces damage to the dies which are of hardened metal and are subjectto breakage.

It is, therefore, a principal object of the invention to provide animproved tube reducing machine having many advantages over thoseheretofore known.

Another object of the invention is to provide a tube reducing machinewith simplified supporting components for die holders thereof whichenable the dies to function with a minimum of sliding.

A further object of the invention is to provide a tube reducing machinewith a drive arrangement which enables operation of the die holders tobe closely coordinated.

Still another object of the invention is to provide a tube reducingmachine with an improved arrangement for synchronizing the strokes ofthe die holders.

Many other objects and advantages of the invention will be apparent fromthe following detailed description of a preferred embodiment thereof,reference being made to the accompanying drawings, in which:

FIG. 1 is a fragmentary side view in elevation of a tube reducingmachine according to the invention, with parts broken away, and ofapparatus for supporting, feeding, and turning a tube being reduced;

FIG. 2 is a fragmentary plan view of the apparatus of FIG. 1;

FIG. 3 is a fragmentary view in vertical cross section, on a greatlyenlarged scale, taken along the line 33 of FIG. 1;

FIG. 4 is a side view in elevation of the tube reducing machine of FIGS.1 and 3, on a slightly smaller scale than FIG. 3, with parts broken awayand with parts in cross section;

FIG. 5 is a right end elevational view of the machine of FIG. 4, withcertain parts removed;

FIG. 6 is an enlarged, fragmentary view in vertical cross section, takenalong the line 6-6 of FIG. 3;

FIG. 7 is a right end view of the components of FIG. 6; and

FIG. 8 is a diagrammatic view showing various lengths and relationshipsbetween several components of the machine embodying the invention.

Referring to FIGS. 1 and 2, a tube reducing machine 10 embodying theinvention is shown with conventional apparatus for feeding and turning atubular billet in coordination with the operation of the tube reducingmachine. This is accomplished through an indexing mechanism 12 whichcoordinates feeding and turning mechanism with the operation of themachine 10. The mechanism 14, through a gear connection 16, issynchronized with a turning mechanism 18 so that the tube is turned atboth ends of the stroke of the machine but is fed longitudinally only atone end of the stroke. The mechanisms 14 and 18 are known in the art andwill not be discussed in detail. A billet 20 usually is from about eightto sixteen feet long prior to being reduced. In a typical example, thebillet 20 initially has a 3 /2 inch diameter which is reduced to 2 /2inches along with a reduction in the thickness of the Wall of the tubefrom /2 inch to 4 inch by the time it emerges from the machine 10. Thetube can be fed axially or longitudinally about 4 inch each time the diecomponents of the machine 10 reach the end of their forward stroke, andthe tube can be rotated typically forty degrees each time the diecomponents reach the end of their rearward stroke. Depending upon theparticular operation, the feed of the tube can vary from about A inch toabout one inch, while the rotation can vary from approximately twentydegrees to sixty degrees. A mandrel is employed within the tube in theconventional manner to control the inside diameter.

Referring more particularly to FIGS. 3-5, the tube reducing machine 10includes a stationary frame 22, an upper die assembly 24, and a lowerdie assembly 26. The stationary frame 22 includes a drive housing orbase 28, side frame members 30 and 32, upper corner posts 34, and anupper frame member 36.

The upper die assembly 24 has an upper axle or backup roll 38 supportedby the upper frame member 36 through ears 40 and 42 and caps 44 and 46.Because the axle 38 is urged upwardly during a tube reducing operation,relatively little stress is placed on the ear caps 44 and 46. Largeroller bearings 48 and 50 are rotatably mounted on spaced cylindricalportions 52 and 54 of the axle 38. A connecting link 56 hasupwardlyextending yokes 58 and 60 rotatably received on the rollerbearings 48 and 50 and provided with suitable covers 62 and 64 extendingaround the bearings 48 and 50. It is not necessary for the yokes 58 and60 to extend completely around the bearings 48 and 50 since most of theforce on the link 56 is in an upward direction. However, the covers 62and 64 serve to retain the yokes 58 and 60 on the bearings 48 and 50 atthe ends of the strokes, when little or no pressure may be applied tothe dies. The link 56 further includes a pair of outboard cylindricalportions 66 and 68 which carry additional roller bearings 70 and 72.Extensions 74 and 76 beyond the cylindrical portions 66 and 68 receivebearing covers 78 and 80 which also extend upwardly around the bearings70 and 72. Further, the link 56 has a cylindrical projection 82projecting beyond the extension 76 to receive an actuator link whichwill be discussed subsequently.

An upper die holder or die block 84 is located below the connecting link56 and has upper yokes 86 and 88 received around and rotatably engagedwith the roller bearings 70 and 72. The outer covers 78 and 80 areaffixed to the die holder 84 and may aid in supporting the die holderfrom the link 56, particularly during end portions of the strokes of thedies. The die holder 84 extends through an included angle of aboutthirty degrees and carries a gear segment 90 at one side which mesheswith a gear segment 92 constituting part of the lower die assembly 26.In turn, the lower gear segment 92 meshes with a gear rack 94 carried bythe frame member 30. This assures coordinated movement of the dieholders of the assemblies 24 and 26 and, at the same time preventspossible slipping of both dies with respect to the tube being reducedand with respect to the frame. This feature of the tube reducing machinecontributes to the overall quality of the product.

The die holder 84 has a central, longitudinal groove or recess 96 inwhich is carried an upper die or die insert 98. The face of the dieinsert 98 is arcuate, similar to that of the die holder 84, but extendsthrough an angle of only about twenty-three degrees compared to aboutthirty-two degrees for the die holder. The face of the die 98 preferablyis recessed slightly from the face of the die holder 84 by about & inchwhich enables much of the pressure to be applied between the die holdersrather than the dies. The slight clearance does not affect the shape ofthe tube being reduced because the die has flared edges extending awayfrom a semicylindrical surface so that the edge portions of the die donot contribute to the forming of the metal even if the dies were incontact. A forming surface 100 of the die is of substantiallysemicircular cross-sectional shape with the radius at the forward end(left end as shown in FIGS. 4 and 6) exceeding that at the rear or rightend. At the forward end, the radius of the die surface 100 issubstantially equal to the radius of the tube or billet to be coldformed and, along a portion of the opposite end is substantially equalto the final desired radius of the tube.

The die 98 is adjustably and accurately located in the die holder groove96 by a mounting assembly shown in FIG. 6, which enables vertical,transverse, and longitudinal adjustment of the die insert. For verticaladjustment, an upper shim 102 is located at the upper wall of the groovewith the die held thereagainst by suitable bolts 104. For transverseadjustment, the groove is provided with a precisely locatedlongitudinal, vertical surface with the die 98 held thereagainst by aside wedge 106 which is adjusted longitudinally by an adjusting bolt 108and a stop bolt 110. For longitudinal adjustment, the die has slantedends which are engaged by two end wedges 112 and 114 verticallyadjustable by bolts 116 and 118. A shim 120 is located between the wedge114 and an end wall 122 of the die holder 84 while a back-up bar 124 islocated behind the wedge 112 and is fastened to the die 98. Theadjustments compensate for wear of the die 98 and also enable closecontrol over the final tube diameter.

Referring to FIGS. 3-5, the lower die assembly 26 includes componentsbasically similar to the components of the upper assembly 24, and willbe discussed in less detail. A lower die or die insert 126, whichincludes a generally semicircular die surface 128 similar to the surface100 of the die 98, is held in a die holder 130 and is recessed thereinabout inch to provide a slight spacing of about inch from the die 98.The die holder 130 is substantially identical to the die holder 84 and,as discussed before, carries the gear segment 92 which engages both thegear segment 90 and the gear rack 94 to assure coordinated movement withthe die holder 84 and also to prevent slipping of both dies relative tothe tube or the frame.

The die holder 130 has a pair of downwardly-extending yokes 132 and 134which are rotatably supported on a pair of roller bearings 136 and 138with covers 140 and 142 extending therearound and aflixed to the dieholder 130. The roller bearings 136 and 138 are mounted on cylindricalportions 144 and 146 of a lower connecting link 148. The link 148 hasdownwardly-ex- 5 tending yokes 150 and 152 supported on roller bearings154 and 156 with covers 158 and 160 extending therearound. The bearings154 and 156 are mounted on cylindrical end portions 162 and 164 of alower axle or backup roll 166.

The axle 166 has a central cylindrical bearing portion 168 which isrotatably mounted on a bearing block 170 having a cap 172. The block 170is supported on an adjusting wedge 174 which is longitudinally movableby an adjusting bolt 176 (FIG. 4) to place a predetermined preload onthe die holders. A substantial pre-load force is required to preventseparation of the die inserts. For example, for a 3 /2 inch diametertube with a /2 inch wall thickness, a force of at least 300,000 poundsis required, depending upon the type of material being processed, toreduce the outside tube diameter to 2%. inches with a inch wallthickness. The bearing block and bearing are further supported throughend supporting blocks 178 and 180 (FIG. 4) and shim plates 182 and 184to provide a broader base for the machine components during operationthereof.

Further support for the die components of the lower assembly can beprovided through two cam followers or rollers 186 and 188 rotatablyconnected by axles 190 and 192 to lower corner portions of the lower dieholder 130. Associated with the cam rollers 186 and 188 are two camplates 194 and 196 suitably aflixed to the frame 30 and contoured suchas to closely follow the paths of the rollers 186 and 188 during therocking movements of the die holders 84 and 130. Actually, the contoursare such that the cam rollers usually do not contact the cams duringmost of the rocking movements but are primarily intended as back-upsupports, if necessary, at the ends of the strokes of the die holders.At the ends of the strokes, less of the weight and forming pressuretends to be carried directly through the connecting links, bearings, andback-up rolls.

Referring now to the drive arrangement for the machine 10, preferablyonly one of the two die assemblies 24 and 26 is driven, with the otherone of the die assemblies then driven through a connection between theassemblies. This eliminates the necessity of coordinating separatedrives as well as reduces the costs of the drive elements and theoverall space requirements for the machine. As shown in FIGS. 3-5, theupper die assembly 24 has a side actuator link 198 having anintermediate opening rotatably receiving the link projection 82 with theactuator link having an upper opening pivotally receiving a projection200. The lower end of the link 198 is pivoted to a drag link 202 whichis pivotally connected to an ear 204 of a slide 206. The slide 206 isreceived on a slide bar or way 208 and has a flange 210 affixed theretowhich is received in a groove 212 in the slide bar 208. Below the slidebar 208, the slide 206 has an ear 214 which is pivotally connected to alower drag link 216. The lower drag link is connected to a loweractuator link 218. This link, at an intermediate point, receives aprojection 220 of the link 148 and, at a lower end, receives aprojection 222 of the axle or back-up roll 166. This drive connectionenables one of the die assemblies 24 and 26 to be driven by the otherand yet enables the die holders to rock back and forth and even toseparate slightly during the pivotal movement of the actuator links 198and 218.

In the specific embodiment shown, the lower die assembly 26 is drivenand for this purpose, the lower die holder 130 has a pair of forwardlyextending arms 224 to which are pivotally connected a pair of crank arms2216 (see FIGS. 4 and These, in turn, are connected eccentrically togears 228 which are driven through gears 230, a drive shaft 232, and asheave 234 connected by belts 236 to a suitable motor 238.

By employing the proper dimensions for the connecting links 56 and 148and the die holders 84 and 130, the dies can be driven back and forththrough their strokes and be maintained under the proper pressurewithout moving the supporting frame 20 relative to the tube and withsubstantially no slipping. Referring to FIG. 8, this result is achievedby designing the supporting links and die holders so that the arc of theaxis of the bearing portion of the connecting link 56, which arc isproduced as the link 56 pivots around the back-up roll 38, issuperimposed on part of a prolate trochoidal curve which would be formedby a point corresponding to the same axis of the link during rotation ofthe die insert 98. As long as the arcuate path of the link axis issubstantially superimposed on the prolate trochoidal curve, the dieinsert 98 will roll along a straight line without any transversemovement of the roll 38 or the frame 22. The

same is equally true for the lower connecting link and die holder. Itmay be noted that the diameter of the die and die holder always exceedsthe distance from the meeting die holder faces to the pivotal connectionof the connecting link and holder as Well as to the pivotal connectionof the connecting link and upper frame.

By way of a specific example, in order to achieve a stroke length ofapproximately 26 inches with the dies 98 and 126 having a radii R1 of 60inches, it is necessary that they rotate through an angle of 23. Bypositioning the axis of the bearing portion of the lower end of the link56 at a point 36 inches from the center of rotation of the die 98, withthe distance D1 then being 24 inches, and by making the effective lengthof the link 58 16% inches long so that the radius R2 is 16% inches, thedesired result is achieved, namely that the are formed by the connectinglink axis will be substantially superimposed on the prolate trochoidalcurve through an arc of 11.5 on each side of the vertical. Beyondapproximately ll.5, the arc of the link axis will deviate above theprolate trochoidal curve and the pressure of the dies 98 and 126 willdiminish; consequently, the dies will separate upon continued angularmovement of the links. Of course, the various factors involved such asstroke lengths, link lengths, angles, etc. will vary for eachapplication and, according to the circumstance, it may be desirable tostart with other given dimensions rather than stroke length as was donein the above example. The angular and length relationships of the upperdie assembly are equally true for the lower die assembly 26.

The above discussion suggests that the arc of the lower axis of the link56 will be directly superimposed on part of the prolate trochoidal curveformed by the same axis or point during the die stroke. Actually,however, the two curves will not be strictly superimposed and it is notessential that they need be. It is important, though, that the arc andthe curve will be superimposed or cross one another at the completion ofthe forward end of the stroke of the dies since this is Where the rearend portions of the dies 98 and 126 determine the final diameter of thetube. The die surface does not taper completely from one end of the die96- to the other, but the last two or three inches of the die,corresponding to the last two or three degrees of the stroke, aresemi-cylindrical and do not taper. It is at these portions of the strokeand the die where the two curves must be substantially identical insofaras the distance from the axis of the axle 38 is concerned, to assureaccurate and true dimensions of the finished reduced tube.

Under the specific conditions discussed, with the radius R2 of the linkbeing 16% inches and with the complete die stroke extending through anarc of 23, the arc and the prolate trochoidal curve must intersect at apoint located 16% inches from the axis of the axle 38 and 11.5 from acenter line through the axle 38, this point being marked P in FIG. 8.The distance from the prolate trochoidal curve to the axis of the axle38 will be less than the radius R2 for angles between 0 and This is oflittle consequence, however, since it merely affects the intermediatediameter of the tube being reduced at portions between the originaldiameter and the final reduced diameter and does not affect the finaltube diameter.

By designing the linkages to relieve the die pressure at the end of eachstroke, when the distance from the axle axis to the lower link axis isless than the distance from the axle axis to the corresponding point ofthe prolate trochoidal curve, the tube can be fed longitudinally androtated at the appropriate ends of the strokes. In the example discussedabove, the dies can be moved through a 26 are with pressure relieved asthe dies move beyond each end of a 23 arc to provide the properclearance, about A; inch in this instance, for axial and rotationalmovement of the tube. Otherwise, the dies 98 and 126 can be machined sothat relief is achieved at the ends of the strokes to the feeding androtation of the tube, by slightly flaring the ends of the die recesses100 and 128.

Various modifications of the above described embodiment of the inventionwill be apparent to those skilled in the art, and it is to be understoodthat such modifications can be made without departing from the scope ofthe invention, if they are within the spirit and the tenor of theaccompanying claims.

I claim:

1. A tube reducing machine comprising a stationary frame, a pair ofopposed die holders, a large diameter die carried by each of saidholders, link means pivotally connected to the upper die holder andpivotally connected to an upper portion of said stationary frame forsupporting said upper die holder and its die by the upper portion ofsaid frame, said link means guiding the center of its pivot connectionwith said upper die holder in an arcuate path lying substantially on aportion of a prolate trochoidal curve traced by the pivot center as thesurface of the upper die holder rolls along a straight line, second linkmeans pivotally connected to the lower die holder and pivotallyconnected to a lower portion of said frame for supporting said lower dieholder and its die by the lower portion of said frame, said second meansguiding the center of its pivot connection with said lower die holder inan arcuate path lying substantially on a portion of a prolate trochoidalcurve traced by the pivot center as the surface of the lower die holderrolls along a straight line, and means carried by said die holders andengageable with one another to coordinate the movement of said dieholders and said dies.

2. A tube reducing machine according to claim 1 characterized byactuator link means movable with said upper link means and loweractuator link movable with the lower link means, and means connectingsaid actuator links.

3. A tube reducing machine according to claim 1 characterized further bycam means mounted on said frame, and cam follower means carried by saidlower die holder for engaging said cam means during a portion of themovement of said lower die holder.

4. A tube reducing machine according to claim 1 characterized by theradii of said upper and lower die holder surfaces exceeding the distancefrom said surfaces to the pivotal connections of said link means andsaid frame.

5. A tube reducing machine comprising a frame, a pair of opposed dieholders having opposed arcuate faces, cooperating dies carried by saiddie holders, means movably connecting said upper die holder to an upperportion of said frame, means movably connecting said lower die holder toa lower portion of said frame, means for rocking said die holders inforward and rearward strokes with the faces of said die holders meetingalong a straight line during the forward and the rearward strokes, meanson each of said die holders engageable with one another to coordinatemovement of said die holders during said forward and rearward strokes,and additional means carried by said frame and engageable with one ofsaid coordinating means to minimize the possibility of both of said dieholders slipping with respect to said frame.

6. A tube reducing machine comprising a frame, a pair of opposed dieholders having opposed arcuate faces,

cooperating dies carried by said die holders, means movably connectingsaid upper die holder to an upper portion of said frame, means movablyconnecting said lower die holder to a lower portion of said frame, meansfor rocking said die holders in forward and rearward strokes with thefaces of said die holders meeting along a straight line during theforward and the rearward strokes, said rocking means comprising meansfor rocking one of said die holders and means connected between said dieholders to cause said one die holder to move the other die holder.

7. A tube reducing machine according to claim 6 wherein said connectingmeans between said die holders includes a slide movable in a directionparallel to the line along which the die holder faces meet, and linkmeans connecting the die holders with said slide.

8. A tube reducing machine comprising a frame, a pair of opposed dieholders having opposed arcuate faces, cooperating dies carried by saiddie holders, means movably connecting said upper die holder to an upperportion of said frame including first link means pivotally connected tosaid upper die holder and pivotally connected to the upper portion ofsaid frame, means movably connecting said lower die holder to a lowerportion of said frame including second link means pivotally connected tosaid lower die holder and pivotally connected to the lower portion ofsaid frame, an upper actuator link pivotally connected to both of thepivots of said first link means and extending downwardly toward theupper die, a lower actuator link pivotally connected to both of thepivots of said second link means and extending upwardly toward the lowerdie, means movably connected to both of said upper and lower actuatorlink to coordinate movement of said actuator links and said die holders,and means for rocking said die holders in forward and rearward strokeswith the faces of said die holders meetin along a straight line duringboth the forward and the rearward strokes, including means for drivingone of said die holders.

9. A tube reducing machine according to claim 8 wherein said meansconnecting said actuator links includes a slide, means for guidablysupporting said slide along a path parallel to the straight line, andlink means connecting said slide to each of said actuator links.

10. A tube reducing machine according to claim 9 wherein said means forrocking one of said die holders includes an arm affixed to one of saiddie holders, a crank arm pivotally connected to said arm, and means fordriving said crank arm.

11. A tube reducing machine comprising a frame, a pair of opposed dieholders having opposed arcuate faces, cooperating dies carried by saiddie holders, means movably connecting said upper die holder to an upperportion of said frame, means movably connecting said lower die holder toa lower portion of said frame, means for rocking said die holders inforward and rearward strokes with the faces of said die holders meetingalong a straight line during the forward and the rearward strokes,arcuate gear segments carried by each of said die holders and engageablewith one another to coordinate movement of said die holders, and a gearrack carried by said frame and engageable with one of said arcuate gearsegments to minimize the possibility of both of said holders slippingwith respect to said frame.

12. A tube reducing machine comprising a frame, a pair of opposed dieholders having opposed arcuate faces, cooperating dies carried by saiddie holders, means movably connecting said upper die holder to an upperportion of said frame, means movably connecting said lower die holder toa lower portion of said frame, means for rocking said die holders inforward and rearward strokes with the faces of said die holders meetingalong a straight line during the forward and the rearward strokes, twospaced cam followers carried by said lower die holder, and cams carriedby said frame for engaging said cam followers and for aiding insupporting said lower die holder at portions of the strokes thereof.

13. A tube reducing machine comprising a stationary frame, a pair ofopposed large diameter die holders, each of said die holders having arecess therein, a die having slanted end faces received in each of saidrecesses, a wedge at each end of said die and engageable therewith,means for adjustably connecting said wedges to the associated die holderwhereby the Wedges can be moved in and out relative to the die holder tomove the die longitudinally thereof to a predetermined position relativeto the die holder, upper link means pivotally connecting the upper dieholder to an upper portion of said frame, lower link means pivotallyconnecting the lower die holder to a lower portion of said frame, meansfor rocking said die holders together in forward and rearward strokeswith said die holders meeting along a straight line which substantiallysymmetrically extends between said dieholders, the radii of the meetingfaces of said die holders exceeding the distance from the meeting diefaces to the axes of the pivotal connections of said link means and saidframe.

References Cited UNITED STATES PATENTS Re. 12,516 7/1906 Briede 721892,118,224 5/1938 Pearson 72189 2,153,839 4/1939 Liebergeld 72-1892,247,863 7/ 1941 Tiedemann 72--189 CHARLES W. LANHAM, Primary ExaminerL. A. LARSON, Assistant Examiner

